Are there any open source sprite format?

PNG just plainly sucks. I has no support for animations, timing or delta compression and sequence names. Also, PNG is slow at random access (you have to decompress image before use). Proprietary formats (like Diablo 2 DCC) are much better, but highly specialized for their games: some have no true color, other have no directions.

I take it you haven't heard that you can root it, and that a recent version of the PS3 SDK is available from pirate sites? Or if you want to go legit on the PSN Store, that the official dev-kit only costs $3000.